1. Field of the Invention
The present invention generally relates to devices which provide velocity control of high pressure flowing fluids, both liquids and gases.
2. Description of the Prior Art
In the handling of flowing high pressure fluids, it has been customary to utilize orifice means having a high velocity short throat section to attain energy losses or high pressure drops. If the fluid is in a liquid state and liable to flash, that is, vaporize or turn to a gaseous condition on the downstream side of the orifice or valve opening, it may condense implosively and induce damaging shock waves, cause erosion, and the like. Also, as the velocity of the fluid in the valve exceeds the velocity of the fluid in the line, several disturbing reactions occur. The most serious problem is rapid erosion of the valve seat plug by direct impingement of the liquid and any foreign particles suspended therein. Additional erosion results from cavitation. Cavitation may be defined as the high speed implosion of vapor against the valve trim and body.
In addition to the severe problems resulting from erosion, the increased velocity also causes the flow characteristics of the valve to become unpredictable and erratic. This occurs because the changes in velocity significantly affect the valve vena contracta vortexes and fluid enthalpies.
Other objectional problems created by the high fluid velocity in the valve are severe noise generation, trim fatigue and possible degradation of flowing fluid materials such, for example, as polymers.
The foregoing and other deficiencies were somewhat overcome by more recent devices which affect dissipation of energy of a flowing high pressure fluid by subdividing it into a plurality of passageways and labyrinths in which there are rapid changes of direction. An example of such devices may be found in U.S. Pat. No. 3,514,074 and 3,513,864. These devices are formed as a series of cylindrically stacked members having inlets and outlets formed along concentric circular peripheries of each member with a labyrinth being formed there between.
Fluid borne noise downstream of control valves is very high. If not treated or contained within a pipe, this noise can result in sound pressure levels of 110 to 170 dB three feet from the valve exit. Sound sources of this magnitude are hazardous, to personnel and frequently result in complaints from local residents.
Mufflers and silencers can only attenuate fluid borne noise 20 to 30 dB. Therefore, only partial success has been achieved with them in obtaining desired sound pressure levels.
Furthermore, a typical path treatment system i.e., the muffler, lagging support structure etc is very cumbersome and expensive, often, the total cost of path treatment can exceed the valve cost many times over.